Wireless Signals

Wireless Signals

1. Radio Refraction and Interference

   • Radio waves are reflected and refracted in the Earth's atmosphere.
     • Amount of refraction depends on the frequency of the wave.
     • Less refraction at higher frequencies.
   • Radio stations broadcast signals with a particular frequency
   • The same frequency can be used by more than one Radio station.
     • If the Radio stations are too far apart from each other to interfere.
     • In unusual weather conditions, radio waves can travel further and the broadcasts interfere.
   • Interference is reduced is digital signals are used.
   • DAB provides a greater choice of radio stations but the audio quality is not as good as FM signals.
   • DAB eliminates interference between other radio stations.

2. Radio Reflection

   • Radio waves are reflected from the ionosphere. Behaves like light form optical fibre and undergo TIR.
   • Water reflects radio waves but land doesn't.
   • Continued reflection by ionosphere and water allows radio waves to be received from an aerial which is not in line of sight.
   • Microwaves pass through the ionosphere.
   • Microwave signals are received by orbiting satellites, amplified and re-transmitted back to Earth.
   • Communication satellites orbit above the equator and take up to 24 hours to orbit the Earth.

3. Communication Problems

   • Radio waves are diffracted when they meet an obstruction.
   • Refraction in the atmosphere needs to be taken into account when sending a signal to a satellite.
   • The transmitting aerial needs to send a focused beam to the satellite because it's aerial is very small.
   • The transmitted beam is slightly divergent.
   • Some energy is lost from the edge of the transmitting aerial because of diffraction.